Abstract:
Many streams in eastern Oregon are listed as water quality impaired on the
basis of water temperature. However, it is often difficult to predict water
temperature for these streams even if there are no anthropogenic impacts. We
measured air and water temperature and stream characteristics on three Type C and
E channel streams to determine if stream type can help predict stream thermal
characteristics. All six streams were hydrologically intact, assessed as Proper
Functioning Condition (PFC), and were located in eastern and south central
Oregon.
Water and air temperatures and stream geomorphic data were taken during
the summer months of 1998 and 1999. Average daily maximum and minimum
water temperature and average daily maximum and minimum rates of change in
water temperature following normalization of data with estimated water residence
time were analyzed. There was more variation within stream type than across
groups, which precluded separation of stream types based on thermal
characteristics. Most streams regardless of type and year exhibited similar daily mean nighttime recoveries of approximately 0.53°C/hour cooling in the
downstream direction following normalization by water residence time. All of the
streams heated at least 1.0°C/hour during the day with some streams gaining
2.25°C/hour in the downstream direction following normalization by water
residence time. Thermal variation among the streams was likely a result of the
daily initial water temperature, the gradient between stream and thermal
environment, and the varied physical character of each stream within type.
Atmospheric temperature is probably the single most critical factor for
characterizing stream temperature behavior during the periods of heating and
cooling.
